Study On Mechanism And Experiment Of Cavitation And Reflection Enhancement By High Pressure Water Jet Grading

With the increase of coal production demand and the entering of coal mining into deep areas,gas accidents pose a great threat to the safety production of coal mines.Through literature investigation and comparison of the current main coal seam anti-reflection and pressure relief technologies,it is believed that the high-pressure water jet cavitation technology has the advantages of short construction period and high safety factor.Theoretical analysis,ground simulation cavitation test and numerical simulation were used to study the effect of pressure relief and reflection improvement of high-pressure water jet grading cavitation.Finally,field tests were carried out in Hongyang No.2 Mine to verify the anti-reflection effect of this process on coal seam.First of high pressure water jet coal mechanism research,based on the investigation of a large number of related literature at home and abroad,summarized the current mechanism of high pressure water jet coal related theory,from the perspective of the structure of water jet and mechanical properties of coal,the process is divided into high pressure water jet coal impact dynamic load effect and quasi static pressure to break the coal phase,This paper introduces the research results of stress wave coal breaking theory,quasi-static elastic coal breaking theory,cavitation coal breaking theory and crack propagation coal breaking theory on different stages of coal breaking mechanism.Theoretical calculation and similar physical experiments were used to select cavitation parameters.The water jet structure and coal breaking effect of nozzles with diameters of 1.5mm,2.0mm,2.5mm and 3.0mm under pump pressure of 25MPa were tested respectively.Solid materials with similar physical properties to coal 12 of Hongyang No.2 Mine were selected to build ground simulation drilling holes.Through the simulated cavitation test,the first-level cavitation radius is 0.6m,and the second-level cavitation radius is 0.9m,which provides a modeling basis for the numerical simulation of reflection improvement effect observation after cavitation.FLAC^3D software was used to study the stress distribution of coal body around each level of cavitation cavity.The results show that the horizontal pressure relief radius of borehole is about 4.5m after secondary cavitation.COMSOL Multiphysics software was used to study the coal gas flow around the cavitation cavities at all levels.By analyzing the distribution and variation of the coal gas pressure after cavitation,the anti-reflection effect of the cavitation cavities at all levels was compared.The results showed that the anti-reflection effect of the second-level cavitation cavity was better,and the coal seam burst elimination could be realized in a shorter time.Finally,in the third mining area of the south wing of Hongyang No.2 Mine-780floor roadway,the construction of graded caving through boreholes is carried out.The first-level caving radius is 0.68m,and the second-level caving radius is 1.03m.After the observation of drainage effect,the gas extraction volume of single hole after second-level caving is 2.52 times that ofφ94mm,and the gas concentration of single hole is 2.87 times that ofφ94mm.The anti-reflection effect of high pressure water jet grading cavitation technology on coal seam is verified.